Method and apparatus for performance metric compatible control of data transmission signals

Abstract

The DC offset of a differential signal can be changed by differentially shifting the DC offset of each of its signals. Techniques are presented for changing, in a controlled way, the DC offset of a differential signal as received by a receiver of a data transmission system. Several classes of example embodiments, utilizing digitally controllable voltage or current sources, are presented. The classes differ based upon such factors as coupling capacitor arrangement and use of termination resistors. Specific embodiments, within each class, differ based upon such factors as whether voltage or current sources are used and the characteristics of such sources. Once the DC offset of a differential signal has been changed, the effect of such change on a performance metric can be measured. Example applications include the ability to determine a differential signal level that results in BER having a particular level and determination of differential signal margin.

1. A method for determining a non-normal signal level for a symbol which produces a non-normal symbol-error-rate in a data transmission system, the method comprising:
 receiving a differential input signal at a DC offset circuit, wherein the differential input signal encodes the symbol, and wherein a differential output signal of the DC offset circuit is provided as input to a receiver; and 
 determining the non-normal signal level for the symbol by using the DC offset circuit to change a DC offset of each signal in the differential input signal by a different amount so that a symbol-error-rate measured by the receiver is substantially equal to the non-normal symbol-error-rate. 
 
     
     
       2. The method of  claim 1 , wherein the DC offset circuit uses a digitally controllable voltage source. 
     
     
       3. The method of  claim 1 , wherein the DC offset circuit uses a digitally controllable current source. 
     
     
       4. The method of  claim 1 , wherein the non-normal signal level is used to estimate the data transmission system's symbol-error-rate under normal operating conditions. 
     
     
       5. The method of  claim 1 , wherein the differential input signal is received through coupling capacitors which are coupled with a transmitter. 
     
     
       6. A hardware apparatus for determining a non-normal signal level for a symbol which produces a non-normal symbol-error-rate in a data transmission system, the apparatus comprising:
 a receiver; 
 a DC offset circuit which receives a differential input signal, wherein the differential input signal encodes the symbol, and wherein a differential output signal of the DC offset circuit is provided as input to the receiver; and 
 circuitry to determine the non-normal signal level for the symbol by using the DC offset circuit to change a DC offset of each signal in the differential input signal by a different amount so that a symbol-error-rate measured by the receiver is substantially equal to the non-normal symbol-error-rate. 
 
     
     
       7. The hardware apparatus of  claim 6 , wherein the DC offset circuit includes a digitally controllable voltage source. 
     
     
       8. The hardware apparatus of  claim 6 , wherein the DC offset circuit includes a digitally controllable current source. 
     
     
       9. The hardware apparatus of  claim 6 , wherein the non-normal signal level is used to estimate the data transmission system's symbol-error-rate under normal operating conditions. 
     
     
       10. The hardware apparatus of  claim 6 , wherein the differential input signal is received through coupling capacitors which are coupled with a transmitter. 
     
     
       11. A computer-based system for determining a non-normal signal level for a symbol which produces a non-normal symbol-error-rate in a data transmission system, the computer-based system comprising:
 a receiver; 
 a DC offset circuit which receives a differential input signal, wherein the differential input signal encodes the symbol, and wherein a differential output signal of the DC offset circuit is provided as input to the receiver; 
 a processor; and 
 a non-transitory computer-readable storage medium storing instructions that when executed by the processor cause the computer-based system to determine the non-normal signal level for the symbol by using the DC offset circuit to change a DC offset of each signal in the differential input signal by a different amount so that a symbol-error-rate measured by the receiver is substantially equal to the non-normal symbol-error-rate. 
 
     
     
       12. The computer-based system of  claim 11 , wherein the DC offset circuit uses a digitally controllable voltage source. 
     
     
       13. The computer-based system of  claim 11 , wherein the DC offset circuit uses a digitally controllable current source. 
     
     
       14. The computer-based system of  claim 11 , wherein the non-normal signal level is used to estimate the data transmission system's symbol-error-rate under normal operating conditions. 
     
     
       15. The computer-based system of  claim 11 , wherein the differential input signal is received through coupling capacitors which are coupled with a transmitter.